http://nova.newcastle.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:10687 In two-choice tasks the preceding sequence of stimuli robustly influences both the P3 ERP component and reaction time (RT) to the current stimulus. We examined sequenceeffects in both two-choice and Go/NoGotasks to distinguish between inhibition and conflict accounts of the N2 and P3 components. RT results suggested similar subjective expectancies were generated in the Go/NoGo and two-choice task. N2 was increased for all unexpected stimuli, even when no response inhibition was required, consistent with a conflict interpretation. The Go/NoGoP3 results also suggested a conflict explanation, and that this conflict was reduced if the response had been recently performed. These results support a reconsideration of the roles of N2 and P3 in all inhibition and conflicttasks, and the Go/NoGotask in particular. 2012-07-03T01:30:05.906Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:3792 The cued Go/NoGo task elicits response preparation during the foreperiod, and, depending on the S2 signal, either response execution or inhibition. This study aimed to determine how processes in the foreperiod might affect or predict post-S2 processing. Thirty-two adults participated in a cued Go/NoGo task (50% Go), with a median split of mean RT producing “Fast” and “Slow” groups. ERP measures were subjected to both ANOVA and regression techniques. There were no differences in the NoGo N2 effect related to response speed, nor was the effect related to pre-S2 processes. The anterior shift of the NoGo P3 was larger in the Fast group, and while the late CNV was associated with the absolute amplitude of both Go and NoGo P3, it was not related to the anterior–posterior Go/NoGo differences. Together, these data suggest that the inhibitory process may be reflected in the NoGo P3 effect, rather than the NoGo N2 effect. 2010-05-12T01:50:01.447Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:3280 Methyl 2-[N-(2′-pyridylmethyl)carbamyl]pyridine-6-carboxylate (H1), prepared by reaction of a 1:1 ratio of the methyl diester of pyridine-2,6-dicarboxylic acid and 2-aminomethylpyridine, can form 1:2 M:L complexes by acting as a tridentate ligand, as exemplified by a crystal structure analysis of [Co|||(1)₂](ClO4) where each ligand is coordinated by the amido group and its two flanking pyridine groups, with the ester group, a relatively poor donor, remaining unbound. The acid formed upon ester hydrolysis, hydrogen 2-[N-(2′-pyridylmethyl)carbamyl]pyridine-6-carboxylate (H₂2), has been isolated as the ammonium salt, and forms a 2:2 M:L dimer [Cu||₂(2)₂(OH₂)₂] where each ligand binds to one copper through the amido group, its flanking pyridine groups, and to the other copper by the carboxylate group, to form a 10-membered ring that incorporates both metals. Onward reaction of the monoester (H1) with a different amine leads to potentially pentadentate ligands centred on a 2,6-disubstituted pyridine but with unsymmetrical arms, as exemplified by synthesis of 2-[N-(2′-pyridylmethyl)carbamyl]-6-[N-(2′-pyridylethyl)carbamyl]pyridine (H₂3), 2-[N-(2′-pyridylmethyl)carbamyl]-6-[N-(1′-piperidinethyl)carbamyl]pyridine (H₂4), and 2-[N-(2′-pyridylmethyl)carbamyl]-6-[N-(2′-hydroxypropyl)carbamyl]pyridine (H₂5). Study of possible helicate formation with the unsymmetrical ligands has been initiated, with the ability to form polymetallic species probed by an ESI-MS study. 2010-04-27T05:07:26.282Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:3791 Objective: Previous event-related potential (ERP) research on inhibitory functioning in attention-deficit/hyperactivity disorder (AD/HD) has often failed to use tasks which optimally assess inhibition. We report on an improved measure of inhibitory function, involving inhibition of a prepotent response, in children with AD/HD. Methods: Twelve males with AD/HD and 12 control males, aged 7–12 years, completed a cued Go/NoGo task where Go stimuli were presented on 70% of trials. ERP and behavioural measures were collected, together with reading, spelling and full-scale IQ scores. Results: The behavioural performance of children with AD/HD was not significantly different from normal controls, although children with AD/HD made faster responses and more errors. Group differences were apparent in the early processing components (P1, N1, P2) of responses to Warning, Go and NoGo stimuli. For the frontally maximal N2, a NoGo>Go effect was found, consistent with previous work linking this component with inhibitory processing. In control children this effect was particularly strong in the right frontal region, while children with AD/HD showed a much larger NoGo>Go effect, and an earlier N2 peak, than controls, with a focal shift to the left frontal region. Conclusions: Compared with normal controls, children with AD/HD demonstrate early stimulus processing atypicalities, suggesting problems with sensory registration and identification of stimuli. Further, N2 results suggest that children with AD/HD must trigger the inhibition process earlier and more strongly than controls to perform at a comparable behavioural level. Significance: The results support the theory that behavioural inhibition is deficient in AD/HD, as children with AD/HD show abnormalities in inhibitory ERP components relating to the effort involved in inhibiting a prepotent response. 2010-04-27T04:57:15.434Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:3794 Objective: The contribution of movement-related potentials (MRPs) to the Go/NoGo N2 and P3 ‘inhibitory’ effects is controversial. This study examined these components in overt and covert response inhibition tasks. Methods: Twenty adult participants counted or button-pressed in response to frequent (60%) and rare (20%) Go stimuli in a Go/NoGo task with equiprobable rare (20%) NoGo stimuli. Results: The N2 NoGo effect did not differ between Count and Press responses, but the P3 NoGo effect was amplified during the Press task. Additionally, subtraction of the ERP waveform for Count NoGo from Press NoGo trials revealed a positivity between 200 and 400 ms, occurring maximally over the central region, contralateral to the responding hand. This difference wave became significant at 210–260 ms, close to the estimated time taken to stop an overt response. Conclusions: The N2 NoGo effect may reflect a non-motoric stage of inhibition, or recognition of the need for inhibition, while the NoGo P3 may overlap with a positive MRP occurring specifically on trials where overt motor responses must be inhibited. Significance: The study confirms that the N2 and P3 NoGo effects are not solely due to movement-related potentials, and posits the NoGo P3 as a marker of motor inhibition. 2010-04-27T04:57:11.336Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:3793 Objectives: In the Go/NoGo task, the N2 and P3 components are often thought to index response inhibition, or conflict between competing responses. If so, they should be affected by response preparation when the prediction of an informative cue is incorrect. Methods: Twenty-six adult participants completed a cued-Go/NoGo task. Targets required a left or right button press, or no response, while cues predicted the probable identity of the target. Analyses examined (a) effects of cues on response preparation, and ‘‘inhibitory’’ components to NoGo targets, (b) typical Go/NoGo differences, and (c) the impact of cue (in)validity. Results: A reaction time benefit was associated with valid cueing, and a cost with invalid cueing. Late CNV results indicated that participants used cue information to prepare responses, and the P3, but not the N2, showed an increase with prior preparation. Typical frontal N2 and P3 NoGo > Go effects were observed, and the P3 but not the N2 showed an Invalid > Valid effect. Conclusions: The P3, rather than the N2, reflects the inhibition of a planned response and/or the conflict between competing responses. Significance: The findings suggest the need for a major review of current interpretations of the N2 and P3 in inhibitory tasks. 2010-04-27T04:57:09.016Z ]]>